Tropical Cyclone Discussion

179
WTPZ42 KNHC 290835
TCDEP2
 
Tropical Storm Vance Discussion Number  32
NWS National Hurricane Center Miami FL       EP222026
200 AM MST Thu Oct 29 2026

Vance has had an unusual structure overnight.  While obviously still 
a sheared tropical cyclone on satellite imagery, scatterometer data 
indicated that strong winds of about 40 kt were located well 
northeast (over 120 n mi) of the center under very deep convection, 
just downstream of the Islas Marias.  This atypical pattern of winds 
very distant from the center suggests that they were probably 
downdraft induced (or convective scale), possibly enhanced by 
terrain and not representative of the tropical cyclone, especially 
with rising pressures observed from the drifting buoy very near the 
center.  There were a couple of believable tropical-storm-force 
vectors closer to the center outside of the thunderstorm mass, so 
the initial intensity is set to 35 kt on this advisory.  

The storm hasn't moved much since the last advisory, with the 
center generally moving north-northeastward slowly.  Basically all 
of the model guidance suggest that the very strong shear will cause 
any deep convection to cease later today.  The evolution would 
cause the system to become very shallow, and it could get caught in 
any area of lighter low-level steering currents, keeping the system 
just offshore of Mexico before it likely degenerates into a trough 
of low pressure later on Friday. The new forecast is nudged to the 
left, toward the model consensus.  

While Vance has re-strengthened slightly, extremely strong vertical 
shear is expected to strip away any remaining associated convection 
later today and cause weakening before the winds could impact 
Mexico.  The new NHC forecast is similar to the previous one and is 
consistent with the latest ECMWF solution, which has had a good 
handle on the temporary re-intensification.  It should be emphasized 
that the main threat with Vance is the very heavy rainfall and high 
rain rates near the areas of very deep convection near the Islas 
Marias and southwestern Mexico.
 
 
Key Message:
 
1. Periods of heavy rainfall associated with Vance will impact
portions of western Mexico during the next day or two. This rainfall
may produce flooding and mudslides across central and southern
Sinaloa, far southwestern Durango, and far northwestern Nayarit,
especially in areas along steep terrain.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  29/0900Z 21.0N 108.4W   35 KT  40 MPH
 12H  29/1800Z 22.0N 108.0W   30 KT  35 MPH
 24H  30/0600Z 23.4N 108.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 36H  30/1800Z...DISSIPATED